Pulsed Electrolysis: Performance Evaluation By Nonlinear Frequency Response Method

Introduction to Chemical Reactor Analysis

Nonlinear frequency response analysis of forced periodic operations with simultaneous modulation of two general waveform inputs with applications on adiabatic CSTR with square-wave modulations

The dynamic optimization of promising forced periodic processes has always been limited by time-consuming and expensive numerical calculations. The Nonlinear Frequency Response (NFR) method removes these limitations by providing excellent estimates of any process performance criteria of interest. Recently, the NFR method evolved to the computer-aided NFR method (cNFR) through a user-friendly software application for the automatic derivation of the functions necessary to estimate process improvement. By combining the cNFR method with standard multi-objective optimization (MOO) techniques, we developed a unique cNFR–MOO methodology for the optimization of periodic operations in the frequency domain. Since the objective functions are defined with entirely algebraic expressions, the dynamic optimization of forced periodic operations is extraordinarily fast. All optimization parameters, i.e., the steady-state point and the forcing parameters (frequency, amplitudes, and phase difference), are determined rapidly in one step. This gives the ability to find an optimal periodic operation around a sub-optimal steady-state point. The cNFR–MOO methodology was applied to two examples and is shown as an efficient and powerful tool for finding the best forced periodic operation. In both examples, the cNFR–MOO methodology gave conditions that could greatly enhance a process that is normally operated in a steady state.

Proton exchange membrane water electrolyzer (PEMWE) takes a central place in the hydrogen economy as a crucial technology for green hydrogen production. However, this technology still faces challenges, such as the cost of the materials, performance losses at high current densities, and durability. To overcome these obstacles, better comprehension of the phenomena occurring in the PEMWE is necessary. Typical electrochemical methods, such as polarization curves and high-frequency response measurements, lack detailed information about the individual contributions to the overall voltage losses and cannot point out the causes of the performance shortcomings. Therefore, the development of advanced diagnosis techniques for PEMWE is of importance both for the state of health analysis during the operation, as well as for the testing of new materials.In this work, a nonlinear frequency response (NFR) method was applied for the diagnosis of a lab-scale PEMWE. The NFR method represents an extension of the electrochemical impedance spectroscopy to the nonlinear domain by investigating the second-order frequency response function (FRF) in addition to the first-order FRF (equivalent to the impedance) [1]. Typical features corresponding to processes occurring in the PEMWE were observed in both the first- and the second-order FRFs. The experimental observations were interpreted based on a simple nonlinear model. The features observed at frequencies higher than 0.1 Hz were attributed to the electrochemical half-reactions, while a high current density feature observed at lower frequencies, could be attributed to the mass transport. During the analysis, the first-order FRF (impedance) was found not to be sensitive enough for the discrimination of the different sets of parameters and the second-order FRF had to be included for better parameter identification. The obtained parametrized model is dynamic and nonlinear and, thus, it can be utilized for model predictive control of the PEMWE and optimization of the overall green hydrogen production system.[1] Vidaković-Koch, T., Miličić, T., Živković, L.A., Chan, H.S., Krewer, U., Petkovska, M., Cur. Opin. Electrochem., 2021, 30, 100851

Nonlinear frequency response analysis of forced periodic operation of non-isothermal CSTR using single input modulations. Part II: Modulation of inlet temperature or temperature of the cooling/heating fluid

Nonlinear frequency response analysis of forced periodic operation of non-isothermal CSTR using single input modulations. Part I: Modulation of inlet concentration or flow-rate

Nonlinear frequency response method for estimation of single solute adsorption isotherms. Part II

The nonlinear frequency response (NFR) method, which is an analytical, fast, and easy method for evaluating the performance of forced periodically operated chemical reactors, was used to investigate possible improvements to a nonisothermal continuous stirred tank reactor (CSTR) when inlet concentration and/or flow rate is periodically modulated. The product yield corresponding to periodic operation is defined, expressions for its estimation, based on the NFR method, are derived, and it is used to evaluate the performance improvements due to periodic operation. Part I considers the general nonisothermal case. In Part II, these results are applied to an adiabatic CSTR and used to evaluate possible improvements for the case of the hydrolysis reaction of acetic anhydride.

A better grasp of the underlying phenomena occurring in electrochemical technologies is crucial for their further development and, consequently, a much-needed step forward to a greener economy. Diagnostic methods that can reliably determine the state of health and causes of the performance shortcomings are indispensable. The ease of obtaining electrochemical data makes the analysis of current and voltage responses the preferred diagnostic approach. Traditional techniques, like steady-state polarization and electrochemical impedance spectroscopy are limited by their inability to distinguish between different processes due to the constraints of steady-state and linearity of system response, respectively. The nonlinear frequency response (NFR) method is an advanced diagnostic method that has the potential to overcome these issues. In this work, the NFR method was applied both experimentally and theoretically to study polymer electrolyte membrane water electrolysis (PEMWE). The model-based analysis provides insights into the losses in the PEMWE at different current densities. It shows that the contributions of the cathode to the overpotential losses at high current densities cannot be neglected. This has been much discussed in the literature and was often attributed only to mass transport losses. The contribution of mass transport has also been identified at higher current densities but is less pronounced than the kinetic contributions. Furthermore, we show that including the nonlinear dynamics in the analysis was crucial for identifying the appropriate parameter set. Overall, this work showed a considerable potential of the NFR method for the diagnosis of PEMWE due to its prospects of identifying different processes occurring within.

The Nonlinear Frequency Response (NFR) method is a useful Process Systems Engineering tool for developing experimental techniques and periodic processes that exploit the system nonlinearity. The basic and most time-consuming step of the NFR method is the derivation of frequency response functions (FRFs). The computer-aided Nonlinear Frequency Response (cNFR) method, presented in this work, uses a software application for automatic derivation of the FRFs, thus making the NFR analysis much simpler, even for systems with complex dynamics. The cNFR application uses an Excel user-friendly interface for defining the model equations and variables, and MATLAB code which performs analytical derivations. As a result, the cNFR application generates MATLAB files containing the derived FRFs in a symbolic and algebraic vector form. In this paper, the software is explained in detail and illustrated through: (1) analysis of periodic operation of an isothermal continuous stirred-tank reactor with a simple reaction mechanism, and (2) experimental identification of electrochemical oxygen reduction reaction.

Estimation of single solute adsorption isotherms applying the nonlinear frequency response method using non-optimal frequencies

Determination of competitive adsorption isotherms applying the nonlinear frequency response method: Part II. Experimental demonstration

Some practical aspects of nonlinear frequency response method for investigation of adsorption equilibrium and kinetics

Electrostatic precipitator (ESP) is the main equipment for flue dust control of coal‐fired power plants in China, accounting for about 70% of the total currently. In this paper, energy efficiency data of ESP, including 202 sets before ultra‐low emission and 45 sets after ultra‐low emission are systematically studied and analyzed by using the research method of field testing and technical investigation. The results showed that after ultra‐low emission, the energy consumption and converted CO2 emission of ESP in coal‐fired power plants increased significantly, and the specific power consumption and energy consumption corresponding to unit mass particulate matter (PM) removal increased by 49.61% and 139%, respectively, and the converted CO2 emission increased by 1.67 × 10−4 kg CO2/m3 and 31.12 kg CO2/t PM on average. The energy consumption of low‐low‐temperature ESP (LLT‐ESP) was positively correlated with its emission reduction range. Before and after the gas cooler operation, the power consumption, specific power consumption and energy consumption corresponding to unit mass PM removal increased by 8.06%–38.68%, 10.66%–60.14% and 7.23%–62.98%, respectively, and the CO2 emissions corresponded increased by 26.29–691.81 kg CO2/h, 0.46–2.18×10−4 kg CO2/m3, 1.10–23.62 kg CO2/t PM, respectively. LLT‐ESP had a great possibility to optimize the operation for energy‐saving and carbon‐reduction, because when the high voltage power supply operated on the maximum output mode and the energy‐saving mode, the drop of power consumption and specific power consumption was around 52.00%–58.23%, 52.02%–58.29%, respectively, and the CO2 emission reductions corresponded was 1,039.25–1,359.35 kg CO2/h, 2.71–3.58×10−4 kg CO2/m3, respectively. LLT‐ESP also had the great optimizing possibility for energy‐saving and carbon‐reduction during low load operation, as when the load reduced from 100% to 50%, the specific power consumption and energy consumption corresponding to unit mass PM removal increased by 5.05%–45.50%, 6.59%–63.90%, respectively, and the CO2 emissions corresponded increased by 0.38–2.44×10−4 kg CO2/m3, 6.76–45.98 kg CO2/h, respectively. The operation energy consumption can be effectively reduced by integrated use of multiple electric dust removal technologies, such as compared with LLT‐ESP technology, the power consumption, specific power consumption and energy consumption corresponding to unit mass PM removal of “low‐low‐temperature + moving electrode+ electrostatic agglomeration” decreased by 37.88%, 30.08% and 45.29% respectively, and the corresponding CO2 emission decreased by 697.22 kg CO2/h, 1.87×10−4 kg CO2/m3 and 32.98 kg CO2/t PM, respectively. The current national standard GB 37484‐2019 is no longer applicable to the energy efficiency evaluation of the ESP in ultra‐low emission units. This study can provide data support for the revision of national standard GB 37484‐2019 and the collaborative efficiency of coal power plant pollution reduction and carbon reduction. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.

Relevance. Currently, oil fields in Russia are mainly developed using the method of artificial maintenance of reservoir pressure to achieve high oil recovery. The use of artificial impact on productive formations by the method of water injection contributes to the premature irrigation of production wells. Water content of productive layers in oil fields significantly complicates the technology of oil production. With the increase in water content of the surface fluid, the power consumed by the engine increases. Minimization of energy consumption is quite relevant, as oil is produced with significant expenditures of electrical energy. It is important to investigate the dependences of the electric energy consumption on the well water cut. Aim. To study the dependence of energy consumption of submersible electric centrifugal units operated in oil production wells on water cut. Methods. Submersible electric centrifugal installations for oil production. Results. In order to study the effects of formation water cut on electrical energy specific consumption, wells with a water cut of more than 90% were selected. Using the formula, the authors have calculated the electrical energy specific consumption for oil production. The analysis of the results of the calculated data showed that in producing wells with a water cut of up to 90 %, the average specific electric power consumption for oil production is within the recommended standards. In wells with the water cut more than 90%, the average specific electric power consumption for oil production exceeds recommended specific norms of electric energy consumption during operation of oil producing wells equipped with electric centrifugal installations. Based on calculated data, the dependence of the specific electrical energy consumption for oil production on the water cut of reservoir products was plotted, and wells with a water cut of more than 90% were selected. The analysis of the graphical dependence showed that in wells with an oil water cut of more than 90%, the specific energy consumption reaches maximum values ​​(the specific energy consumption increases by 40%).